Memory cells having a plurality of resistance variable materials

ABSTRACT

Resistance variable memory cells having a plurality of resistance variable materials and methods of operating and forming the same are described herein. As an example, a resistance variable memory cell can include a plurality of resistance variable materials located between a plug material and an electrode material. The resistance variable memory cell also includes a first conductive material that contacts the plug material and each of the plurality of resistance variable materials and a second conductive material that contacts the electrode material and each of the plurality of resistance variable materials.

PRIORITY INFORMATION

This application is a Continuation of U.S. application Ser. No.15/617,381, filed Jun. 8, 2017, which is a Continuation of U.S.application Ser. No. 15/245,249 filed Aug. 24, 2016, now U.S. Pat. No.9,679,641, which is a Continuation of U.S. application Ser. No.14/596,293 filed Jan. 14, 2015, now U.S. Pat. No. 9,449,683, which is aDivisional of U.S. application Ser. No. 13/570,772 filed Aug. 9, 2012,now U.S. Pat. No. 8,964,448, the specification of which is incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memoryapparatuses and methods, and more particularly to resistance variablememory cells having a plurality of resistance variable materials.

BACKGROUND

Memory devices are utilized as non-volatile memory for a wide range ofelectronic applications in need of high memory densities, highreliability, and data retention without power. Non-volatile memory maybe used in, for example, personal computers, portable memory sticks,solid state drives (SSDs), digital cameras, cellular telephones,portable music players such as MP3 players, movie players, and otherelectronic devices.

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory, including random-access memory (RAM),read only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), flash memory, and resistancevariable memory, among others. Types of resistance variable memoryinclude phase change random access memory (PCRAM) and resistive randomaccess memory (RRAIVI), for instance.

Resistance variable memory devices, such as PCRAM devices, can include aresistance variable material, e.g., a phase change material, forinstance, which can be programmed into different resistance states tostore data. The particular data stored in a phase change memory cell canbe read by sensing the cell's resistance e.g., by sensing current and/orvoltage variations based on the resistance of the phase change material.

Some resistance variable memory cells can store multiple units, e.g.,bits of data. Such memory cells can be referred to as multilevel cells.Multilevel memory cells can provide for increased storage capacity of amemory device, while providing for a decreased physical footprint ascompared to memory devices having single level cells, among otherbenefits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a portion of an array of resistancevariable memory cells in accordance with a number of embodiments of thepresent disclosure.

FIGS. 2AX and 2AY illustrate cross-sectional views of a portion of anarray of resistance variable memory cells in accordance with a number ofembodiments of the present disclosure.

FIGS. 2BX-2IY illustrate various process stages associated with forminga resistance variable memory cell in accordance with a number ofembodiments of the present disclosure.

DETAILED DESCRIPTION

Resistance variable memory cells having a plurality of resistancevariable materials and methods of operating and forming the same aredescribed herein. As an example, a resistance variable memory cell caninclude a plurality of resistance variable materials located between aplug material and an electrode material. The resistance variable memorycell also includes a first conductive material that contacts the plugmaterial and each of the plurality of resistance variable materials anda second conductive material that contacts the electrode material andeach of the plurality of resistance variable materials.

Embodiments of the present disclosure can provide multilevel resistancevariable memory cells having a compact cell architecture. In a number ofembodiments, the resistance variable memory cells can be verticallyoriented and have a 4F² architecture, with “F” corresponding to aminimum feature size. As such, embodiments can provide improved storagedensity and improved scalability as compared to previous approaches,among other benefits.

In the following detailed description of the present disclosure,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration how a number of embodimentsof the disclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical,and/or structural changes may be made without departing from the scopeof the present disclosure.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining digits identify an element or component in the drawing.Similar elements or components between different figures may beidentified by the use of similar digits. For example, 102 may referenceelement “2” in FIG. 1, and a similar element may be referenced as 202 inFIG. 2, e.g., FIG. 2AX. Also, as used herein, “a number of” a particularelement and/or feature can refer to one or more of such elements and/orfeatures.

FIG. 1 is a schematic diagram of a portion of an array 102 of resistancevariable memory cells in accordance with a number of embodiments of thepresent disclosure. The array 102 includes a number of resistancevariable memory cells 104, each including a select device 106 coupled toa resistance variable storage element 108. The memory cells 104 can beformed in accordance with embodiments described herein.

The resistance variable storage elements 108 can include a resistancevariable material, e.g., a phase change material. The resistancevariable material can be a chalcogenide e.g., a Ge—Sb—Te material suchas Ge₂Sb₂Te₅, Ge₁Sb₂Te₄, Ge₁Sb₄Te₇, etc., among other resistancevariable materials. The hyphenated chemical composition notation, asused herein, indicates the elements included in a particular mixture orcompound, and is intended to represent all stoichiometries involving theindicated elements. Other resistance variable materials can includeGe—Te, In—Se, Sb—Te, Ga—Sb, In—Sb, As—Te, Al—Te, Ge—Sb—Te, Te—Ge—As,In—Sb—Te, Te—Sn—Se, Ge—Se—Ga, Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, In-Sb—Ge,Te—Ge—Sb—S, Te—Ge—Sn—O, Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co,Ge—Sb—Te—Pd, Ge—Sb—Te—Co, Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te,Ge—Sn—Sb—Te, Ge—Te—Sn—Ni, Ge—Te—Sn—Pd, and Ge—Te—Sn—Pt, for example. Ina number of embodiments, the resistance variable material can be a metaloxide material such as TiO₂, La₂O₃, LaAlO₃, Ga₂O₃, ZrO₂, ZrxSiyO₂,Zr_(X)Ti_(Y)O_(Z), IIfO₂, IIf_(X)Ti_(Y)O_(Z), SrTiO₃, LCMO, MgO,Al_(X)O_(Y), SnO₂,ZnO₂, Ti_(X)Si_(Y)O_(Z), and/or a hafnium siliconoxide Hf_(X)Si_(Y)O_(Z), among other metal oxide materials.

The select devices 106 may be field effect transistors, e.g. metal oxidesemiconductor field effect transistors (MOSFETs), a bipolar junctiontransistor (BJT) or a diode, among other types of select devices.Although the select device 106 shown in FIG. 1 is a three terminalselect device, the select devices can be two terminal select devices,for instance.

In the example illustrated in FIG. 1, the select device 106 is a gatedthree terminal field effect transistor. As shown in FIG. 1, a gate ofeach select device 106 is coupled to one of a number of access lines105-1, 105-2 . . . , 105-N, e.g., each access line 105-1, 105-2, . . . ,105-N is coupled to a row of memory cells 104. The access lines 105-1,105-2, . . . , 105-N may be referred to herein as “word lines.” Thedesignator “N” is used to indicate that the array 102 can include anumber of word lines.

In the example illustrated in FIG. 1, each resistance variable storageelement 108 is coupled to one of a number of data/sense lines 107-1,107-2, . . . , 107-M, e.g., each data line 107-1, 107-2, . . . , 107-Mis coupled to a column of memory cells 104. The data/sense lines 107-1,107-2, . . . , 107-M may be referred to herein as “bit lines.” Thedesignator “M” is used to indicate that the array 102 can include anumber of bit lines. The designators M and N can have various values.For instance, M and N can be 64, 128, or 256. However, embodiments arenot limited to a particular number of word lines and/or bit lines.

The select devices 106 can be operated, e.g., turned on/off, toselect/deselect the memory cells 104 in order to perform operations suchas data programming, e.g., writing, and/or data sensing, e.g., readingoperations. In operation, appropriate voltage and/or current signals,e.g., pulses, can be applied to the bit lines and word lines in order toprogram data to and/or read data from the memory cells 104. As anexample, the data stored by a memory cell 104 of array 102 can bedetermined by turning on a select device 106, and sensing a currentthrough the resistance variable storage element 108. The current sensedon the bit line corresponding to the memory cell 104 being readcorresponds to a resistance level of the resistance variable material ofresistive storage element 108, which in turn may correspond to aparticular data state, e.g., a binary value. The resistance variablememory array 102 can have an architecture other than that illustrated inFIG. 1, as will be understood by one of ordinary skill in the art.

In a number of embodiments of the present disclosure, the array 102 canhave a 4F² architecture, e.g. the resistance variable memory cells 104of the array 102 can have a 4F² footprint. Also, the resistance variablememory cells 104 may be vertical memory cells and can be formed, forinstance, as described further herein, e.g., in connection with FIGS.2B1-2I2.

The access lines and the data/sense lines can be coupled to decodingcircuits formed in a substrate material, e.g, formed below the array andused to interpret various signals, e.g., voltages and/or currents, onthe access lines and/or the data/sense lines. As an example, thedecoding circuits may include row decoding circuits for decoding signalson the access lines, and column decoding circuits for decoding signalson the data/sense lines.

As used in the present disclosure, the term “substrate” material caninclude silicon-on-insulator (SOI) or silicon-on-sapphire (SOS)technology, doped and undoped semiconductors, epitaxial layers ofsilicon supported by a base semiconductor foundation, conventional metaloxide semiconductors (CMOS), e.g., a CMOS front end with a metalbackend, and/or other semiconductor structures and technologies. Variouselements, e.g., transistors, and/or circuitry, such as decode circuitryfor instance, associated with operating the array 102 can be formedin/on the substrate material such as via process steps to form regionsor junctions in the base semiconductor structure or foundation.

FIGS. 2AX and 2AY illustrate cross-sectional views of a portion of thearray 202 of resistance variable cells in accordance a number ofembodiments of the present disclosure. For FIGS. 2AX and 2AY, the “X”following the letter designation indicates a x-cut view, e.g., a viewcorresponding to a direction that is parallel with the data/sense lines107-1, 107-2, . . . , 107-M, discussed with FIG. 1. For FIGS. 2AX and2AY, the “Y” following the letter designation indicates a y-cut view,e.g., a view corresponding to a direction that is parallel with theaccess lines 105-1, 105-2, . . . , 105-N, discussed with FIG. 1.

As mentioned, the array 202 includes a number of resistance variablememory cells 204. FIGS. 2AX and 2AY illustrates portions of resistancevariable memory cells 204-1 and 204-2. Each of the resistance variablememory cells 204-1 and 204-2 include a plurality of resistance variablematerials 210-1, 210-2, 210-3, which serve as storage elements for therespective cells.

In a number of embodiments, the resistance variable materials 210-1,210-2, 210-3 can be phase change materials, e.g., chalcogenides, whichinclude a number of active regions representing portions of theresistance variable materials 210-1, 210-2, 210-3 that undergo phasetransitions, e.g., from crystalline (low resistance) to amorphous (highresistance) and vice versa, in response to heating due to a current flowthrough the material, e.g., during memory cell operation.

In a number of embodiments, the resistance state associated with thememory cells 204-1 and 204-2 can depend on the phase of the respectiveactive regions corresponding to resistance variable materials 210-1,210-2, 210-3. For instance, a lowermost resistance associated with theresistance variable memory cells 204-1 and 204-2 can correspond to eachof the active regions, e.g. of resistance variable materials 210-1,210-2, and 210-3, being in a crystalline phase. An uppermost resistanceassociated with the resistance variable memory cells 204-1 and 204-2 cancorrespond to each of the active regions being in an amorphous phase. Afirst intermediate resistance associated with the resistance variablememory cells 204-1 and 204-2 can correspond to one of the activeregions, e.g., associated with resistance variable material 210-1, beingin an amorphous phase while the active regions associated withresistance variable materials 210-2 and 210-3 are in a crystallinephase, and a second intermediate resistance associated with theresistance variable memory cell 204 can correspond to two of the activeregions, e.g., associated with resistance variable materials 210-1 and210-2, being in an amorphous phase while the active region associatedwith resistance variable material 210-3 is in a crystalline phase. Thedifferent resistance states associated with resistance variable memorycells 204-1 and 204-2 can correspond to different data states, e.g.,binary values, stored by resistance variable materials 210-1, 210-2,210-3. For instance, the lowermost resistance state can correspond tobinary “11”, the uppermost resistance state can correspond to binary“00”, and the intermediate resistance states can correspond to binary“10” and “01”, respectively. Embodiments are not limited to theseparticular data assignments or to two bit memory cells. For instance, ina number of embodiments, each resistance variable memory cell caninclude more than three resistance variable materials such that thecells are programmable to have more than four different resistancestates.

Each of the plurality of resistance variable materials 210-1, 210-2,210-3 has a respective thickness 212. For instance, in the exampleillustrated in FIGS. 2AX and 2AY, resistance variable material 210-1 hasa thickness 212-1, resistance variable materials 210-2 has a thickness212-2, and resistance variable materials 210-3 has a thickness 212-3. Asillustrated in FIGS. 2AX and 2AY each of the resistance variablematerials 210 can have a different thickness 212. However, embodimentsare not so limited. For example, a number of the resistance variablematerials 210 can have a thickness that is the same as the thickness ofanother resistance variable material 210. In a number of embodiments,the resistance variable materials can have a same thickness but can bedifferent resistance variable material or a same resistance variablematerial with a different stoichiometry.

The active regions associated with the resistance variable materials 210may transition from a crystalline phase to an amorphous phase, forinstance, responsive to an applied programming voltage, e.g., a voltagedifference between a plug material and an electrode material, asdiscussed further herein. As discussed, each of the resistance variablematerials 210 can have a different thickness 212, as such the activeregions may transition from the crystalline phase to the amorphousphase, for instance, responsive to different applied programmingvoltages. For instance, an active region associated with the resistancevariable material 210-3 having a greater thickness 212-3, as compared tothe thicknesses 212-2 and 212-1 of resistance variable materials 210-2and 210-1, may transition to an amorphous phase responsive to arelatively lower applied programming voltage than active regionsassociated resistance variable materials 210-2 and 210-1 havingrelatively lesser thicknesses 212-2 and 212-1.

As such, a programming voltage can be determined which is sufficient toeffect transition of active region of resistance variable material 210-3from a crystalline phase to an amorphous phase but which is insufficientto effect transition of active regions of resistance variable materials210-2 and 210-1 to the amorphous phase. Similarly, a programming voltagecan be determined which is sufficient to effect transition of activeregions of resistance variable materials 210-3 and 210-2 from acrystalline phase to an amorphous phase but which is insufficient toeffect transition of the active region of resistance variable material210-1 to the amorphous phase. Also, a programming voltage can bedetermined which is sufficient to effect transition of each of theactive regions of resistance variable materials 210-3, 210-2, and 210-1from a crystalline phase to an amorphous phase. Additionally, aprogramming voltage can be determined which is insufficient to effecttransition of the active regions of the resistance variable materials210-3, 210-2, and 210-1 from a crystalline phase. The differentprogramming voltages can be applied to cell 204 in order to program thecell 204 to one of a number of target data states, e.g., four datastates (11, 10, 01, and 00) in this example. In accordance a number ofembodiments of the present disclosure, a thickness 212 of a resistancevariable material 210 may be a tuning parameter for the cell 204. Forinstance, the thicknesses 212-1, 212-2, 212-3 of the plurality ofresistance variable materials 210-1, 210-2, 210-3 can be tuned toachieve different programming voltages necessary to induce a phasechange of the active regions discussed herein. However, embodiments arenot so limited. For example, in embodiments in which the resistancevariable material includes a metal oxide, a programming voltage can bedetermined which is sufficient to cause ion, e.g., oxygen ion for metaloxide materials, vacancy movement. For example, a programming voltagecan be determined which is sufficient to cause ion vacancy movement forresistance variable material 210-1, a programming voltage can bedetermined which is sufficient to cause ion vacancy movement forresistance variable materials 210-1 and 210-2, and a programming voltagecan be determined which is sufficient to cause ion vacancy movement forresistance variable materials 210-1, 210-2, and 210-3.

Although the embodiment illustrated in FIGS. 2AX and 2AY illustrates a2-bit memory cell 204, e.g., a cell programmable to four data states,embodiments are not so limited. For instance, the resistance variablememory cell 204 can include more (or less) than the three resistancevariable materials 210-1, 210-2, 210-3. That is, the cell 204 caninclude additional resistance variable materials vertically spaced apartfrom the resistance variable materials 210-1, 210-2, 210-3. Forinstance, cell 204 could include seven resistance variable materialssuch that the cell is programmable to eight different data states, e.g.,a 3-bit cell, or cell 204 could include two resistance variablematerials such that the cell is a 1.5-bit cell. As such, the storagedensity of the cell 204 can be increased while maintaining a 4F²footprint, for example. The additional resistance variable materials canhave a thickness that is different than a number of the thicknesses212-1, 212-2, 212-3. However, embodiments are not limited as such. Forexample, a number of the additional resistance variable materials canhave a thickness that is the same as a number of the thicknesses 212-1,212-2, 212-3.

As shown in FIGS. 2AX and 2AY, a resistance variable memory cell 204 caninclude a plug element, e.g., formed from a plug material 214. In anumber of embodiments, the plug material 214 can be coupled to a selectdevice corresponding to a resistance variable memory cell 204, e.g., aselect device such as select device 106 shown in FIG. 1. In a number ofembodiments, the plug material 214 can be a conductive material.However, embodiments are not so limited. For example, in a number ofembodiments, the plug material 214 can be another material, such assilicon, among other materials.

As shown in FIGS. 2AX and 2AY, a resistance variable memory cell 204 caninclude a contact formed of a conductive material 216, e.g., a heatermaterial. In accordance with a number of embodiments of the presentdisclosure, the conductive material 216 can be an L-shaped electrode,e.g., a heater electrode. For example, the conductive material 216 canhave a first portion that is parallel to the plurality of resistancevariable materials 210 and a second portion that is perpendicular to theplurality of resistance variable materials 210, e.g., the first portionof the conductive material 216 can be perpendicular to the secondportion of the conductive material 216. As illustrated in FIG. 2AY, theconductive material 216 can contact, e.g., be formed on, the plugmaterial 214. However, embodiments are not so limited. For example,another conductive material (not shown) can be formed between theconductive material 216 and the plug material 214. As illustrated inFIG. 2AY, the conductive material 216 contacts each of the plurality ofresistance variable materials 210-1, 210-2, 210-3.

A resistance variable memory cell 204 can include a contact formed of aconductive material 218. As illustrated in FIG. 2AY, the conductivematerial 218 can contact each of the plurality of resistance variablematerials 210-1, 210-2, 210-3 of a first cell 204-1 and each of theplurality of resistance variable materials 210-1, 210-2, 210-3 of asecond cell 204-2. In other words, the conductive material 218 can beshared by two cells, e.g., cell 204-1 and adjacent cell 204-2, of thearray 202.

In a number of embodiments, the resistance variable memory cell 204 caninclude an electrode element formed of an electrode material 220. Asillustrated in FIG. 2AY, the electrode material 220 can be formed on,e.g., contact, the conductive material 218. As an example, the electrodematerial 220 can be, or can be coupled to, a conductive line such as abit line, e.g., bit lines 107-1 to 107-M shown in FIG. 1.

Embodiments of the present disclosure are not limited to the physicalstructure of cell 204 shown in FIGS. 2AX and 2AY. For instance, in anumber of embodiments, the structure of the plug material 214 and/or theelectrode material 220 can be different. Also, contact locations of theplug material 214 and/or the electrode material 220 can be different, aswell as a contact area between the conductive material 216 andresistance variable materials 210 and/or a contact area between theconductive material 218 and resistance variable materials 210.

FIGS. 2BX-2IY illustrate various process stages associated with forminga resistance variable memory cell in accordance with a number ofembodiments of the present disclosure, e.g., a cell such as cells 204-1and 204-2 described in the above discussion of FIGS. 2AX and 2AY.Similar to FIGS. 2AX and 2AY, for FIGS. 2BX-2Y2, the “X” following theletter designation indicates a x-cut view and the “Y” following theletter designation indicates a y-cut view. Embodiments are not solimited. For instance, the designator “X” could correspond to a y-cutview and the designator “Y” could correspond to an x-cut view.

The resistance variable memory cells can be formed using variousprocessing techniques such as atomic material deposition (ALD), physicalvapor deposition (PVD), chemical vapor deposition (CVD), supercriticalfluid deposition (SFD), patterning, etching, filling, chemicalmechanical planarization (CMP), combinations thereof, and/or othersuitable processes. In accordance with a number of embodiments of thepresent disclosure, materials may be grown in situ.

In accordance with a number of embodiments of the present disclosure, amethod of forming a resistance variable memory cell can include forminga plug material 214, as illustrated in FIGS. 2BX and 2BY. The plugmaterial 214 may be a conductive material such as copper, platinum,tungsten, silver, titanium nitride, tantalum nitride, tungsten nitride,and/or ruthenium, among various other materials and/or combinationsthereof. In a number of embodiments, the plug material 214 can beanother material, such as silicon, among other materials.

The plug material 214 may be formed, e.g., patterned, on a dielectricmaterial 222, which can be formed on a substrate material as discussedherein. In accordance with a number of embodiments of the presentdisclosure, dielectric material 222 can be a silicon oxide or siliconnitride, among other dielectric materials, for instance.

A material stack 224 can be formed on the plug material 214 and thedielectric material 222. The material stack 224 can include a number ofalternating resistance variable materials 210 and dielectric materials226, e.g., resistance variable material layers separated by dielectricmaterial layers. The material stack 224, as shown in FIGS. 2BX and 2BY,includes resistance variable materials 210-1, 210-2, 210-3, which areseparated by dielectric materials 226-2 and 226-3. Additionally, asshown in FIGS. 2BX and 2BY, the material stack 224 can includedielectric materials 212-1 and 212-4, which may be utilized to separatea number of the plurality of resistance variable materials 210 fromanother component of the resistance variable cell. For instance, asillustrated in FIGS. 2BX and 2BY, the dielectric material 226-1separates the resistance variable material 210-1 from the plug material214, e.g., the dielectric material 226-1 can be formed on the plugmaterial 214 and resistance variable materials 210-1, 210-2, 210-3 canbe formed on the dielectric material 226-1.

In accordance with a number of embodiments of the present disclosure, amask material 228 can be formed on the material stack 224. For example,as illustrated in FIGS. 2BX and 2BY, the mask material 228 can be formedon the dielectric material 226-4. The mask material 228 can be a siliconnitride material, a polysilicon material, or other material suitable forserving as a mask material during a subsequent processing step.

FIGS. 2CX and 2CY illustrate the material stack 224 of FIGS. 2BX and 2BYat a subsequent processing stage. In FIGS. 2CX and 2CY portions of thematerial stack 224 have been removed, e.g., by patterning and etchingthe material stack 224. In accordance with a number of embodiments ofthe present disclosure, portions of the material stack 224 can beremoved by a double pitch etch. For example, when F is a minimumprintable line, a double pitch etch can be used to obtain 2F trenchesand 2F lines. However, embodiments are not so limited.

FIGS. 2DX and 2DY illustrate the formation of conductive elements 216,e.g., heater electrodes, subsequent to the processing shown in FIGS. 2CXand 2CY. The conductive elements 216 can be formed, for instance, by aconformal deposition of a conductive material over the structure ofFIGS. 2CX and 2CY, such that the conductive material contacts the plugmaterial 214 and each of the plurality of resistance variable materials210-1, 210-2, 210-3. The conductive material 216 can be formed ofvarious conductive materials such as titanium, titanium nitride, siliconcarbide, graphite, tantalum nitride, tantalum-aluminum nitride, tungstennitride, for instance, and/or combinations thereof

As illustrated in FIG. 2DY, a spacer material 230 can be formed on theconductive material 216. The spacer material 230 can be silicon oxide orsilicon nitride, among other spacer materials for instance. Followingformation of the spacer material, portions of the conformally formedconductive material, e.g., conductive material 216, and spacer material230 are removed, e.g., by etching, which separates the conductivematerial 216 in the bit line direction. For example, as shown in FIG.2DY, the spacer material 230 and conductive material 216 are recessed byan amount 232 below an upper surface of dielectric material 226-4.

FIGS. 2EX and 2EY illustrate the structure shown in FIGS. 2DX and 2DYafter a filling process and a planarization process is performed, inwhich a dielectric material 234 is formed over the structure. Forexample, the dielectric material 234 can be formed on the spacermaterial 230, the dielectric materials 222 and 226-4, and the maskmaterial 228. In accordance with a number of embodiments of the presentdisclosure, a planarization process, e.g., CMP, may be performedfollowing formation of the dielectric material 234.

Subsequent to the planarization, for example, the first mask material228 can be removed and a second mask material 236 can be formed on thedielectric material 226-4 and the dielectric material 234, asillustrated in FIG. 2FY. Thereafter, portions of the mask material 236can be removed, e.g., by etching, as illustrated in FIGS. 2GX and 2GY toform spacers 236-1 and 236-2. The spacers 236-1 and 236-2 define a widthof an opening 237. An etch process can then be performed to removeportions of dielectric materials 226-4, 226-3, 226-2, and 226-1 andportions of resistance variable materials 210-3, 210-2, and 210-1 toform a trench (not shown) having a same width as that defined by opening237.

A conductive material 218, as illustrated in FIG. 2HY can be formed inthe trench, as well as on portions of the mask material 236 and thedielectric material 234. The conductive material 218 can contact each ofthe resistance variable materials, e.g., resistance variable materials210-1, 210-2, 210-3, and each of the dielectric materials, e.g., 226-1,226-2, 226-3, 226-4. In accordance with a number of embodiments of thepresent disclosure, the conductive material 218 can be a composite ofmore than a single material, e.g., it can include a barrier (orsidewall) material and a core material.

As illustrated in FIGS. 2IX and 2IY, a portion of the conductivematerial 218, the mask material 236, and the dielectric material 234 canbe removed, e.g., by etching and/or CMP. As shown in FIGS. 2AX and 2AY,a conductive material 220 can be formed on the structure shown in FIGS.2IX and 2IY. The conductive material 220 can serve as and electrodecorresponding to the memory cell. In a number of embodiments, material220 can serve as a conductive line, e.g., a bit line, of the cell. Theconductive material 218 in the trench can serve as a conductive contactbetween the resistance variable materials 210-1, 210-2, 210-3 of thecells 204-1 and 204-2 and the electrode material 220.

The electrode material 220 can be formed by a damascene process, forexample, among other processes. The electrode material 220 can becopper, platinum, tungsten, silver, aluminum, titanium nitride, tantalumnitride, tungsten nitride, and/or ruthenium, among various othermaterials and/or combinations thereof. Also, as shown in FIG. 2AX, anetch can be performed in the y-direction to define individual cells andto define individual conductive lines, e.g., bit lines, of the array.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of various embodiments of the presentdisclosure.

It is to be understood that the above description has been made in anillustrative fashion, and not a restrictive one. Combination of theabove embodiments, and other embodiments not specifically describedherein will be apparent to those of skill in the art upon reviewing theabove description. The scope of the various embodiments of the presentdisclosure includes other applications in which the above structures andmethods are used. Therefore, the scope of various embodiments of thepresent disclosure should be determined with reference to the appendedclaims, along with the full range of equivalents to which such claimsare entitled.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim.

Rather, as the following claims reflect, inventive subject matter liesin less than all features of a single disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

What is claimed is:
 1. A method of forming memory cells, the methodcomprising: forming a first plug material and a second plug material;forming a material stack on a portion of the first plug material and aportion of the second plug material, wherein the material stack includesa plurality of resistance variable materials separated by respectivedielectric materials; forming a first conductive material on the firstplug material, the first conductive material serving as a firstconductive contact for the plurality of resistance variable materials ofa first memory cell; forming a second conductive material that serves asa second conductive contact for the plurality of resistance variablematerials of both the first memory cell and an adjacent memory cell andis separated from the first plug material by a dielectric material,wherein the second conductive material is formed subsequent to formingthe first conductive material; and forming a third conductive materialon the second plug material, the third conductive material serving as afirst conductive contact for the plurality of resistance variablematerials of the adjacent memory cell.
 2. The method of claim 1, whereineach of the plurality of resistance variable materials have differentthicknesses.
 3. The method of claim 1, wherein the first conductivecontact for the first memory cell and the first conductive contact forthe adjacent memory cell comprise respective heater electrodes for thememory cells.
 4. The method of claim 1, wherein forming the secondconductive material includes forming the second conductive materialself-aligned to the first conductive material and to the thirdconductive material.
 5. The method of claim 1, wherein at least two ofthe plurality of resistance variable materials are a same materialhaving different stoichiometries.
 6. The method of claim 1, wherein themethod further comprises forming a bit line material on the secondconductive material.
 7. The method of claim 1, wherein each of theplurality of resistance variable materials comprises a chalcogenidematerial.
 8. The method of claim 1 wherein forming at least one of thefirst and the third conductive material comprises forming an L-shapedelectrode.
 9. An array of memory cells, comprising: a first plugmaterial and a second plug material; a material stack formed on at leasta portion of the first plug material and on at least a portion of thesecond plug material, wherein the material stack includes a plurality ofresistance variable materials separated by respective dielectricmaterials; a first conductive material on the first plug material, thefirst conductive material serving as a first conductive contact for theplurality of resistance variable materials of a first memory cell; asecond conductive material that serves as a second conductive contactfor the plurality of resistance variable materials of both the firstmemory cell and an adjacent memory cell and is separated from the firstplug material by a dielectric material, wherein the second conductivematerial is formed subsequent to forming the first conductive material;and a third conductive material on the second plug material, the thirdconductive material serving as a first conductive contact for theplurality of resistance variable materials of the adjacent memory cell.10. The array of claim 9, wherein the second conductive contact isshared by the first memory cell and the adjacent memory cell.
 11. Thearray of claim 9, wherein the plurality of resistance variable materialsof the first memory cell are formed between a portion of the firstconductive material and a portion of the second conductive material. 12.The array of claim 11, wherein the plurality of resistance variablematerials of the adjacent memory cell are formed between the portion ofthe second conductive material and a portion of the third conductivematerial.
 13. The array of claim 12, wherein the portion of the firstconductive material extends vertically along a sidewall of the firstmemory cell and the portion of the third conductive material extendsvertically along a sidewall of the adjacent memory cell.
 14. The arrayof claim 13, wherein the second conductive material is formed in a viaseparating the plurality of resistance variable materials of the firstmemory cell and the plurality of resistance variable materials of theadjacent memory cell.
 15. The array of claim 9, wherein at least two ofthe plurality of resistance variable materials comprise differentthicknesses.
 16. The array of claim 9, wherein the first plug materialis coupled to a first word line and the second plug material is coupledto a different word line.
 17. The array of claim 16, wherein the secondconductive contact is coupled to a bit line shared by the first memorycell and the adjacent memory cell.
 18. A method of forming an array ofmemory cells, the method comprising: forming a material stack comprisinga plurality of resistance variable materials separated by respectivedielectric materials, wherein the plurality of resistance variablematerials of the material stack are formed between a first heaterelectrode corresponding to a first memory cell and a second heaterelectrode corresponding to an adjacent memory cell; forming a via in thematerial stack, wherein the via separates resistance variable materialsof the first memory cell from resistance variable materials of theadjacent memory cell; and forming, in the via, a conductive contactmaterial that is shared between the first memory cell and the adjacentmemory cell such that the resistance variable materials of the firstmemory cell are formed between the first heater electrode and theconductive contact material and the resistance variable materials of thesecond memory cell are formed between the second heater electrode andthe conductive contact material.
 19. The method of claim 18, furthercomprising forming the conductive contact material subsequently toforming the first heater material and the second heater material. 20.The method of claim 18, further comprising forming the first heaterelectrode on a first plug material corresponding to the first memorycell and forming the second heater electrode on a second plug materialcorresponding to the adjacent memory cell.